Lift as well as forward motion in helicopters is usually provided for by a principle rotor system; the rotor also provides for attitude control. In order to compensate the momentum as well as for controlling the craft around the main vertical axis, secondary tail end rotor is provided whose axis extends perpendicular to the direction of flight. Helicopters of this known type generally have optimum hovering properties but are inferior as compared to regular air foil aircraft, owing to a considerably reduced forward propagation speed; also range and economy of helicopters are inferior to regular aircraft. The reason for the limited forward propagation speed is to be seen in that in case of an increase of that speed the oncoming flow towards the blade that moves in the direction of flight approaches the speed of sound so that the resistance at that blade and in that instance increases rather drastically. On the other hand as the rotor blade moves in the opposite direction the flow will in fact separate over a large area, owing to the large angle of attack of the blades. Moreover, large zones and areas of the rotor blades have to be and are in fact being subjected to an oncoming flow from the rear.
In order to increase the operative range generally towards larger propagation speeds it is basically necessary to overcome the limit which obtains when the reversely moving blades, owing to flow separation, simply can no longer produce the requisite lift. This speed limit can be overcome by forcing flow of pressurized air out of slots in the rotor, particularly the leading and trailing edges thereof so as to obtain a circulation control such that the lift production at and by the rotor blades becomes independent from the flow of air towards the blade in any location. Aircraft using circulation control are basically known. It is also known to provide a control disk for a higher harmonic kind of mechanical control of the pressure medium which control disk is both stationary and flexible and through appropriate control and is being deformed in accordance with prescribed rules.